In the operation of certain amplifiers, an offset voltage may be introduced into the output. If the input signal is very small, then the offset may be much larger than the actual signal. For example, a photodiode will generally produce a very low current. A transimpedance amplifier (TIA) may be used convert the current generated by incident into an output voltage signal. The transimpedance amplifier may be realized through use of a switch capacitor based integrator.
However, a switch based capacitor integrator may add an undesirable supply dependent offset voltage to the output of the amplifier. In this example, the offset is caused by a charge injection from the switch of the integrator circuit. Because the amplifier requires a large gain, a very small capacitor is used, and thus results in a relatively high offset voltage as the capacitor is discharged.
In a system, the offset voltage will generally be subject to further amplification, such by a succeeding programmable gain stage. At higher gain values, the output of the programmable gain stage output offset may include a significant offset voltage.
Even if an offset voltage may then be reduced or eliminated, the voltage generally has introduced non-linearities into the signal, thereby distorting the signal output. Further, the amplified offset voltage may effectively reduce the dynamic range of circuit elements, such as an analog to digital converter element, because of the need to convert a signal that includes a large offset voltage component into a digital value, rather than only converting the smaller value of the actual output signal.